The National Institute of Health estimates 65 percent of Americans are overweight or obese. Out of the millions Americans who are overweight and go on a diet each year, many regain all or a part of the weight they lose within five years.

Still, the search for the miracle weight-loss cure goes on. The reality is that losing weight requires a change in eating habits and a boost in daily physical activity. You must burn more calories than you consume.

For some people, however, prescription weight-loss drugs may help them achieve their weight-loss goal. According to the National Institutes of Health Weight-control Information Network (WIN), weight-loss medications should be used only by very obese people or those who are overweight or obese and have other risk factors for obesity-related illness. The WIN says that these drugs should be used along with a diet and exercise program.

Prescription weight-loss drugs are recommended for people who are obese (those with a body mass index of 30 or greater), or for those who are overweight (those with a BMI of 27 to 29.9) and who suffer from or are at risk for high blood pressure, heart disease or diabetes. These drugs are usually recommended for people who are obese and have been unable to lose weight after making multiple attempts while under the supervision of a health care provider. A safe and reasonable goal for weight loss is 10 percent in six months.

How they work

Prescription weight-loss drugs work in one of two ways. They can suppress the appetite and increase metabolism by altering the activity of chemical brain messengers called neurotransmitters. Drugs that do this are sibutramine, amphetamines and phentermine. A second type of weight-loss drug reduces the body's ability to absorb fat. The drug orlistat works in this way. Your health care provider will determine which kind is best for you by considering your medical history and the potential side effects and interactions of each drug.

Side effects of appetite suppressants include headaches, constipation, back pain, insomnia, dry mouth, nervousness and upset stomach. Sibutramine, amphetamines and phentermine should not be used if you have hypertension, coronary heart disease or glaucoma. Amphetamines should not be used if you have hyperthyroidism. Phentermine, on rare occasions, has been associated with the development of pulmonary hypertension, a fatal lung condition.

Side effects of drugs that affect how the body absorbs fat include oily spotting, gas (flatus) sometimes with discharge, urgency to have a bowel movement, fatty or oily stools and sometimes fecal incontinence. Women may develop menstrual irregularities. People taking orlistat must take a supplemental multivitamin to prevent deficiencies of fat-soluble vitamins.

No magic pill

Prescription weight-loss drugs are not magic potions. The WIN recommends they be used in conjunction with behavior modification and nutritional counseling so you can make long-term changes in your diet and activity patterns. You'll also need to see your health care provider regularly. Studies indicate if you don't lose four pounds in four weeks, it is unlikely the drug will contribute to significant weight loss.

Weight-loss drugs will not keep the weight off forever. Their safety has only been studied over a short period of time. And most studies have found that even with weight-loss drugs, most people will not be able to maintain weight loss over the long term. Drug therapy is only effective when used along with a structured diet and exercise program. Maintaining the weight loss requires a healthy change in lifestyle for the long term. If you don't make lifestyle changes, the weight will return.